1. Field of the Invention
This invention relates to a solid image pickup apparatus and particularly to a solid image pickup apparatus in which photo sensing elements are coupled with a plurality of vertical transfer electrodes and which is capable of outputting signal charges produced by said photo sensing elements by switching a plurality of said vertical transfer electrodes from one electrode to another as the fields are passed through by turns.
2. Description of the Related Art
For solid image pickup apparatuses, various attempts have been made to reduce false signals due to images which exceed Nyquist limits. One result of these attempts is a solid image pickup apparatus proposed in Japanese Patent Disclosure No. 86-133782. This apparatus is provided with a plurality of charge transfer type solid image pickup elements and a plurality of vertical transfer electrodes which are coupled to photo sensing elements at a rate of four electrodes to one photo sensing element. The apparatus outputs signal charges produced by the photo sensing elements by switching the vertical transfer electrodes from one electrode to another as the fields are passed through by turns.
The operation of this apparatus will be described in the following.
The photo sensing elements are arranged in a checkered pattern. Each photo sensing element is coupled with four vertical transfer electrodes through transfer gate zones. A transfer gate zone is provided for one vertical transfer electrode. In a first field, signal charges produced by four photo sensing elements are read by a first Vertical transfer electrode and output. In the next field, signal charges of the four photo sensing elements coupled to a second vertical transfer electrode are read and output. In the same way, signal charges are read and output by a third and a fourth vertical transfer electrode. Thus, an image is composed of signals from four fields. The feature of this image pickup apparatus is that it is possible to realize an optical aperture greater than a picture element pitch given equivalently and eliminate false signals ascribable to images in excess of Nyquist limits.
As described above, each vertical transfer electrode must read signal charges produced by four photo sensing elements. To this end, it is necessary to provide a channel zone as large as possible. In addition, since the photo sensing elements must be arranged in a checkered pattern, the transfer channel width under a vertical transfer electrode is unavoidably narrow at the area in contact with vertical transfer electrodes of the previous and next stages and wide at the central part along the path of electric charge transfer. Consequently, the electric potential is deeper at the central part of each vertical transfer electrode than in the other area. This gives rise to an electric potential pocket for the electric charges, which results in an improper transfer of the electric charge.